Beware of Salifert Alk test kit change

[Battlecorals Verified Sponsor]

This is kind of strange to me. Been using the salifert alk kit for ages now. I go through a couple a month easy. I find it odd that they'd make a nice new color instruction sheet for about a year, then revert back to the same style and format as the old one, but make an adjustment to the procedure. I'm not going to loose any sleep on this one, but I don't get why they ditched the nicer looking color one, unless it was just a cost issue.

 

[Scorpius]

Maybe they found some nice color directions in a corner and figured they'd use them up. lol

 

[Randy Holmes-Farley Verified Community Expert]

I don’t think it’s dye in the Ca kit, I think it’s NaOH if I remember correctly. I assume the dye is the purple granules.

OK, thanks. Sometimes they are combined, but if not, the NaOH amount also is not super critical. It is being used to precipitate magnesium. As long as there is enough to precipitate the magnesium as magnesium hydroxide, that's sufficient, and more isn't going to do much unless there's so much that it is also precipitating calcium hydroxide.

 

[Randy Holmes-Farley Verified Community Expert]

Hey Randy. Appreciate you wading in. Value your input. I will check out your DIY alk test posted prior.

Might adding twice the amount of dye that the instructions call for (the old value of 4 drops rather than the new value of 2 drops) qualify as adding "too much". I did get what I would call significant different values when I ran the test with 2 drops or 4 drops - but maybe I would get different values every time I test just with the margin of error that are inherent to these kits.

I had wondered if the dye was thicker, the drops bigger etc. Going with the old instructions did not seem right to me either. So I was testing as per new instructions. I am wondering now ....

My alk runs pretty stable (measured make-up water w Kalk) and a low demand tank so I was not sweating the difference between test - paying more attention to stability than exact numbers.

I would think a company that sells testing supplies would have a method of being contacted about this sort of thing though ....

I cannot answer how much dye (of unknown concentration) is too much, but it becomes too much if the dye itself takes up too much acid or base and impacts the measured alkalinity. The goal is to have the molar concentration of the dye unimportantly low relative to the alkalinity present.

One of the dyes frequently used as part of such a mixture is bromcresol green. It changes color as it takes up H+, just like alkalinity takes up H+:
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422013000100031